AMICON System Specification draft revision 1.02 April 1980

AMICON SYSTEM SPECIFICATION

Draft Revision 1.01
April, 1980

This is a draft version of specifications for use of the
data communications special service channel (L2) on the
AMSAT Phase III satellite, the communications medium which
serves as the foundation of the AMSAT International
Computer Network (AMICON). This document is subject to
final approval by the Board of Directors of AMSAT. As a
draft document it is subject to discussion, negotiation,
further study, and potential rewrite of major sections.
This document has not been approved for general
publication. The contents herein represent the current
thinking of the authors, and your comments and criticisms

will be most welcome.

Comments and questions should be directed to:
AMICON System Architecture Design Group

c/o

H. S. Magnuski, KA6M, 311 Stanford Ave., Menlo Park, CA 94025

(415) 854-1927

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01

FOREWORD

The Radio Amateur Satellite Corporation (AMSAT, P.O. BOX 27, WASHINGTON,
D-C. 20044) will launch, courtesy of the European Space Agency, their Phase III
satellite sometime during May, 1980. Unlike previous satellites OSCAR 46775, .6;
etcvy; the Phase III machine will be in an orbit permitting extended
communications periods for stations in the coverage area- Effective use of its
70 cm to 2 meter transponder will require more detailed planning and
coordination than with previous OSCAR’s, and a bandplan for the 180 kHz
passband has already been approved by the AMSAT Board of Directors. Part of the
plan makes provisions for six special service channels (General Voice
Bulletins, Education Services, Scientific Services, Traffic, CW/RTTY bulletins
and code practice, and Data Communications). The procedures for use of the Data
Communications Special Service Channel, also known as Special Service Channel
‘Lower 2’ (SSC L2), is the concern of this document.

The explosive growth of the use of computers by radio amateurs, coupled
with the potential of this new communications medium lead to fantastic
possibilities for the establishment of two-way computer links, computer
networks, packet radio gateways for long haul traffic, and even digitized voice
or video. The realization of this potential, however, requires that
communications standards be established so that common equipment and protocols
can be used and shared by all interested operators. The standards must also
consider and be compatible with other users of the spacecraft transponder.
Thus, the contents of this document not only prescribe. frequency assignments
and modulation techniques, but also outline rules for time-shared use of the
channel, packet layout, network protocols and other related matters.

The authors realize that standards are a two-edged sword, and have tried
to obtain a balance between weak standards, which allow development in too many
different directions, and overly restrictive standards, which could stifle
creativity.

Contributors to this document include:

Vern Riportella WA2LQQ AMICON Coordinator

H. S. Magnuski KA6M N. Cal. AMICON Coordinator
Mark Kaufmann WB6ECE Network Design Consultant
Gary Hendra WA6S UW Digital Systems Engineer
Gary Fariss WO6KYF Software Systems Engineer

and many other radio amateurs who have offered constructive criticisms
of the plans detailed herein.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01

PREFACE

Amicon System Specification
for the
AMSAT Phase III Satellite Channel L2

The AMSAT Board of Directors considering

a) that there is an urgent need for a common modulation method
and accepted set of channel usage procedures (Level 1 Interface) ;

b) that there should be a specified format for transmitting
message blocks over the channel (Level 2 Interface) 3

c) that there is a compelling need for coordination among the
stations wishing to transmit and receive messages and files
on the system (Level 3 Interface);

d) that future use of the channel would be greatly enhanced by
commonly agreed to specifications for the most heavily used types
of data communications (Level 4 Interface);

unanimously declares the view

that the following system specifications be adhered to by all
stations using the special service channel for data communications
on the AMSAT Phase III Satellite.

[Note: Text within square brackets in the following document is background
discussion material designed to inform the reader of some of the issues
involved in the design of the specification. It is not part of the formal
document and is subject to deletion once the final draft is approved.

The current practice for specifying network architectures is to define
independent functions in separate groups or layers. This document follows that
design principle by proposing that AMICON be split into four distinct levels.
The first level deals with the transmission channel and defines how a bit
stream is transmitted between two stations. The second level superimposes
characters and blocks of characters on the bit stream. The third level
describes how blocks of characters are routed and sequenced through the
network. The fourth level deals with the transmission of information which may
span multiple blocks and which requires end-to-end checking.]

Digitized by the Internet Archive
in 2025 with funding from
Amateur Radio Digital Communications, Grant 151

httos://archive.org/details/amicon-sys-spec-draft-3

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01

Table of Contents

Chapter 1 - Level 1 Interface: Physical Interface

POL Channel Assignment and Characteristics
1.2 Channel Access and Usage

LES Carrier and Modulation Specifications
1.4 Transmission Timing

Chapter 2 - Level 2 Interface: Packet Transmission

2-1 Packet Framing Specifications

2.2 Transmission Code

2.3 Channel Multiple Access Protocol

2.3.1 Definitions

2.3.2 Control Parameter Notation

2-3-3 Control Using the Simple ALOHA Algorithm
2.3.3.1 Simple ALOHA Transmission Control
2.3.3.2 Simple ALOHA Retransmission Control
Die sa3 Simple ALOHA Control Parameter Values
2.3.4 Control Using the S-ALOHA-CLC Algorithm
2-3-4.1 Closed Loop Control Assumptions
2.3.4.2 Closed Loop Control Algorithm

23. 438 Closed Loop Control Parameter Values

Chapter 3 - Level 3 Interface: Network Specifications

3.1 Datagram Network Characteristics
3-2 Packet Format

3.3 Packet Node Addressing

3.3.1 Packet Node Addressing Syntax
Roe2 Specific Call Group Syntax
3.3.3 General Call Group Syntax
323.4 Call Group Qualifiers

3.3.5 Call Group Addressing Examples
3.4 Packet Data Field

Chapter 4 - Level 4 Interface - Applications

4.1 File Transfer Protocol

4.2 Graphic Standards

4.3 Image and Video Transmission
4.4 Digitized Voice Transmission

Appendix A - Selected Bibliography

Appendix B - ISO Specification 3309

Appendix C Datagram Addressing Syntax Diagram
Appendix D - Distribution List

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 1

Chapter 1

LEVEL 1 INTERFACE: PHYSICAL INTERFACE

1. 1 Channel Assignment and Characteristics

The AMSAT Phase III satellite has one inverting transponder with a 70 cm
uplink and a 2 meter downlink. The bandplan assignment is based on the 2 meter
downlink, which serves as the frame of referencee Subject to final calibration
after launch, the passband center is 435.215 MHz for the uplink, and 145.900
for the downlink. There are two beacons marking the edges of the downlink
passband, the lower "General" beacon at 145.810 MHz, and the upper
"Engineering" beacon at 145.990 Mhz. The special service channels Ll, L2 and L3
are allocated spectrum at 17, 21 and 25 kHz center frequencies above the
General beacon. Channels Hl, H2 and H3 are located at 17, 21 and 25 kHz center
frequencies below the Engineering beacon. The L2 channel has been allocated for
data communications and computer networking (nominally 435.284 MHz uplink,
145.831 MHz downlink).

The originating station must control the 70 cm uplink frequency such that
the 2 meter downlink frequency (as monitored at the originating station) is at
the specified offset from the pilot beacon to within a tolerance of +/- 1.0
kHz. Use of the SSCs with equipment incapable of this tolerance is discouraged.

[The 3 dB bandwidth being specified for the other channels is 2.4 kHz, and
the data communications spectrum will probably have to meet this spec. The 1.0
kHz frequency tolerance was taken from the June 1979 AMSAT Newsletter, and may
prove to be too loose for the L2 channel.]

1.2 Channel Access and Usage

In order to provide maximum channel utilization and _ to eliminate
contention for channel time, a well organized system of coordinators and
procedures is essential. Authority to use the channel comes from the AMSAT
Phase III Operations committee-e The special service channel coordinator member
of the committee will appoint three regional coordinators to deal with channel
usage in their respective regions. The regional L2 coordinator is responsible
for assigning time slots for different modes of operation and L2 usage. Within
a given timeslot, where the modulation and protocol implementations are
compatible, access to the channel will be governed by the algorithms specified
in Chapter 2.

1.3 Carrier and Modulation Specifications

[The selection of a suitable carrier and modulation scheme will be the subject
of some debate within the amateur community, and currently there is no
technique which can be considered the preferred method. The relative
efficiencies of synchronous transmission probably will preclude any
asynchronous modulation method. The following is a list of some of the
considerations which are relevant to use of the L2 channel:

Power budget of the transponder
Channel 3db bandwidth or signalling speed in b/s per Hz.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 2
Level 1 Interface: Physical Interface

Doppler shift

Frequency offset between sequential users of the channel
Eb/No (dB) for the modulation technique

Performance in the presence of cw interference

Channel capture capability

Complexity for the implementation

Cost of implementation and availability of hardware
Regulatory and licensing considerations

Two of the more frequently mentioned techniques are SSB and AFSK-FM. Karl
Meinzer, in the June 1979 AMSAT bulletin, has outlined the use of uncoded PSK
for the telemetry channel of the satellite.

What we really need now is a written proposal covering the three major
modulation methods and an evaluation of each method in terms of the criteria
outlined above. A summary of the principle methods includes:

AM - On-Off Keying with non-coherent detection
Quadrature Amplitude Modulation
Quadrature Partial Response

FM - FSK, non-coherent detection
CP-FSK, continuous phase FSK
MSK, minimum shift keying

PM - BPSK, binary phase shift keying
DE-PSK, differential encoded phase shift keying
QPSK, quaternary phase shift keying
OK-QPSK, offset keyed quternary phase shift keying

A very excellent and current summary of modulation methods for radio work
can be found in ’A Comparison of Modulation Techniques for Digital Radio” by
John D. Oetting, IEEE Transactions on Communications, Vol. COM-27 No. 12,
December, 1979. This article would serve as a good basis for our comparisons of
different schemes.]

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 3
Level 1 Interface: Physical Interface

1.4 Transmission Timing

The following description outlines a typical transmission. The times tO,
tl, »«.- use as a point of reference the output antenna of the transmitting
station. Note that there is a corresponding set of times sO, sl, «+. which may
be referenced at the output antenna of the transponder, and a third set r0, rl,
--- which may be referenced at the receiver.

tO - The transmitter places carrier on the channel.e The transmitter
assumes that the channel is idle and unused prior to t0.

tl - Modulation is placed on the carrier such that all receivers assume a
logical one or marking condition. Note that tl may be the same as t0.

t2 - Denotes the start of the first idle flag or synchronization
character.

t3 - Defines the transition between the last idling or synchronization
character and the first byte of the packet.

t4 - The time at the end of the last checksum or crc byte.

t5 - The time at the end of the last idle flag, syne character or pad
character.e The channel goes into a marking condition.

t6 — The instant that modulation is removed from the carrier. Note that t5
and t6 may coincide.

t7 - The removal of all carrier by the transmitter. This time may coincide
with t6.

All stations must comply with the station identification requirements
imposed by their licensing authority. However, since this channel may be
heavily utilized, the time taken for id should be kept to the minimum allowed.
All cw identification should occur between tO and t3.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 4

Chapter 2

LEVEL 2 INTERFACE: PACKET TRANSMISSION SPECIFICATIONS

2el1 Packet Framing Specifications

The format of the message block or packet transmitted on the channel shall
be in compliance with ISO Standard 3309 ‘High-level Data Link Control
Procedures - Frame Structure.” Use of extended address and control fields, as
detailed in the standard, is not recommended. The information field length
within each packet shall be a multiple of 8 bits.

[The use of HDLC format could be controversial. The standards, techniques and
equipment for the use of true, bit-oriented HDLC are still fairly new to _ the
industrial world. The requirements for constructing an HDLC frame seem
impossibly complex at first, and they would be except for the fact that many
semiconductor companies have designed and are currently selling (for prices in
the $30-$50 range) chips which do all the hard work. Here is a list of
currently available HDLC oriented chips:

Fairchild 3846 Synchronous Data Link Controller
Intel 8273 SDLC/HDLC Protocol Controller
Motorola 6854 Advanced Data Link Controller
Nippon Electric Co. UPD379 SDLC Protocol Controller
Signetics 2652 Multi-protocol Controller
Standard Microsystems 5025 Multi-protocol Controller
Western Digital 1933 Synchronous Data Link Controller
Zilog SIO Serial I/O Controller

The HDLC protocol is being designed into new equipment by all major
manufacturers, and it forms the basis for the new international packet
switching networks. It will be the standard for data communications in the
eighties. If we are in the process of creating a digital networking
specification for use over the next’ ten years, we should build on what is
currently accepted industrial practice, even though most amateurs may be
unfamiliar with the details involved. A group of pioneering Canadian operators
has already conducted experiments using HDLC chips and established an HDLC
beacon on 20 meters, so we have evidence that the technology is not out of
reach of the amateur community. The main drawback with specifying bit-oriented
HDLC is that it is incompatible with commonly used USARTs, such as the 8251A.

Also, note that this spec only calls for frames from the HDLC standard.
The complete HDLC protocol is probably not appropriate for our multiple-access
broadcast oriented packet repeater.]

2-2 Transmission Code

The transmission code used for text characters within the message shall
meet the standards set by C.C.I.T.T. Recommendation V.3 - International
Alphabet No. 5.

[This is the international standard corresponding to ANSI Standard X3.4-1968
“Code for Information Interchange - ASCII.”]

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 5
Level 2 Interface: Packet Transmission Specifications

2-3 Channel Multiple Access Protocol

When channel usage is low, packets may be transmitted using a simple ALOHA
protocol. When utilization becomes heavy, packets will be exchanged on the
channel using an S-ALOHA protocol with closed loop control.

2-3-1 Definitions

A multiple-access-channel is a communications channel where many
transmitting stations can attempt to access a receiving station using a common
transmission medium and equipment. The uplink to the Phase-III satellite is a
multiple-access channel.

A broadcast-channel is a communications channel where many stations can
receive messages from a single transmitting station. The downlink of the Phase-
III satellite is a broadcast channel.

The term carrier-sensed multiple-access channel (CSMA) describes a
situation where each transmitter is able to detect the carrier (presence of an
on-going transmission) from all other transmitters. The Phase III input channel
has this characteristic except for the fraction of a second delay at the
beginning of a transmission when the input signal has to travel to the
satellite and return to receiving groundstations. The use of carrier sensing
improves channel efficiency, particularly for longer packets.

Due to the fact that transmissions are occuring at random with no
centralized control, there is the possibility of overlap of transmitted packets
or collisions, where two or more transmitters are on the air at the same time.
For efficient use of the channel it is important that each station be able to
monitor its translated signal and check the validity of the returned packet
while it is being transmitted. This ability to receive one’s own packets and
validate their contents is called a collision detection capability.

At any given time, using the output antenna of the transponder as our
point of reference, the channel will be either be inactive with no carrier
present or active with carrier. The channel duty cycle is the percentage of
time that the channel is active. This measurement should be made over an
extended period of time, at least 15 minutes or more.

A set of rules and procedures for controlling the exchange of messages on
a communications channel is a communications protocol. Of the many hundreds of
communications protocols currently in use there is a set of protocols, known as
ALOHA protocols, which are concerned with regulating the flow of messages or
packets on communications media where the messages are sent using a multiple-
access channel and received on a broadcast channel. The name “ALOHA” is used
because much of the initial research and the first implementations were done by
the University of Hawaii in the construction of their ALOHA Packet’ Radio
Network.

A simple ALOHA protocol allows any station on the network to transmit
whenever it’s ready. If the transmitted packet is not received correctly, the
transmitter waits some random amount of time and tries again.

A slotted ALOHA protocol (S-ALOHA) requires that all transmissions on the
multiple-access channel be synchronized to start and end within specified time

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 6
Level 2 Interface: Packet Transmission Specifications

periods or slots. All slots are of the same duration and can contain the
maximum length packet. Each transmitter decides on which time slot to use on a
random basis.

A slotted ALOHA closed loop control protocol (S-ALOHA-CLC) allows
transmitting stations to adjust their transmission control parameters to
accomodate varying load conditions on the channel. Each transmitted packet
contains a computed variable which reflects, in part, the success that the
transmitting station is having in sending packets. All receiving stations
monitor this variable and adjust, through use of the algorithms and _ formulas
specified below, their transmit and retransmit controls. Closed loop control of
an ALOHA channel allows throughput to approach theoretically maximum limits,
provides a mechanism for dynamic changes in the control parameters needed to
cope with varying loads, minimizes overall packet delay, and contributes to the
efficient use of the channel under heavy load conditions.

2.3.2 Control Parameter Notation

The notation and control algorithms given below were adapted from a paper
written by Gerla and Kleinrock (see the bibliography, Appendix A). Their
careful study and contribution to the solution of this control problem is
acknowledged.
Specification of the ALOHA control procedures uses the following variables:

n — The number of stations currently actively using the L2 channel.

i - Stations are indexed by the variable “i” where i ranges from 1 to n.

tau - The time in seconds required to transmit a maximum length packet.

ts - The period of a slot in a slotted channel.

W - The history window (measured in slots) maintained by each station.

E - The number of empty slots in W.

S(i) - Successful packets from station i in W.

S - Total successes in We. Computed by summing all S(i) for i= 1 ton.

C(i) - Collisions suffered by station i in W.

C - The total number of collision slots in W.

C =W- (S + E)
C’ - An estimate of the total number of collisions in W.
Cc’ = (C(i)/S(i))*s

m - Average number of collided packets per collision. Note that this
parameter cannot be measured directly through monitoring the channel.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 7
Level 2 Interface: Packet Transmission Specifications

UC - Interval (in slots) between successive updates of control parameters.
Note that UC will be less than or equal to W.

G - Average channel load in window. Computed through the formula:
G = (S+C*m) /W

In the closed loop control algorithm presented below G will only be estimated
because the true value of m is not available.

Gmax - A ceiling value for the G estimate.

Pn(i) - New transmission probability gate value for station i. At each
transmission decision point (the time when a new packet is ready for
transmission in the simple-ALOHA protocol or the time when a new packet is
ready and we have the start of a slot for the slotted-ALOHA protocol) the
transmitter draws a random number ranging from zero to one.e If the number
picked is less than or equal to Pn(i), then transmission commences. For the
simple protocol Pn(i) = 1 and transmission always occurs immediately, providing
the channel is inactive (there is no carrier at the transmit site). The initial
value of “Pn(i)° is’ Pn.

Pr(i) — Retransmit probability “gate” value *for “station "0% Atweaen
transmission decision point Pr(i) is used to determine if a previously
transmitted packet should be retransmitted. Packets will need retransmission if
they are not positively acknowledged by the receiver or if the transmitter
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output. All packets that need retransmission must be sent first before any new
packets are attempted (the retransmit packet queue has a strictly higher
priority than the new packet queue)- In the simple ALOHA protocol the
transmission decision points occur every tau seconds after an error is
detected. In the S-ALOHA protocol there is a decision point at the beginning of
each slot. The, initial value of Pr(i) is* Pr’

Prmax -— Ceiling value for Pr(i).

P - The weighted average of all current gate values. The value P is
computed by summing Pn(i)*S(i) for all i and dividing by S- The value of Pn(i)
is contained in a control byte in each transmitted packet. S(i) is obtained by

monitoring the channel and is based on successfully received packets.

DP - The gate value increment. This parameter is used to compute the new
values of Pn(i) and Pr(i) and controls their rate of change.

2.3.3 Control Using the Simple ALOHA Algorithm

If the channel duty cycle is less than 20% there is no justification for
requiring closed loop control and simple control procedures will suffice. The
protocol, in its most basic form, follows these two steps:

1. When a station has a new packet ready to transmit, it transmits it.

2. If the packet was not received correctly, the station waits some
random amount of time and then retransmits the packet.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 8
Level 2 Interface: Packet Transmission Specifications

The following paragraphs will clarify some of the details concerning the above
two steps.

La se saul Simple ALOHA Transmission Control

First, in this section and the next we differentiate between new packets
and ones that have been previously transmitted. The probability of transmission
control gates Pn(i) for new packets and Pr(i) for retransmitted packets have
different values. Pn(i) for this protocol is always 1, implying that
transmission will be immediate. Pr(i) will be assigned a value when the network
starts up, and may be subject to change as the load grows-e The priority of
packets due for retransmission is strictly higher than that of new packets. We
will also restrict each station to have only one unconfirmed packet in the air
at any given time- Due to the round-trip signal delays involved, in theory it
is not absolutely essential that stations hold back transmissions if there is
already carrier present on the output channel. The carrier may already be off
at the transmitter site using the channel. Carrier sensing will, however,
improve throughput, so it is recommended that new transmissions not start if
the channel is already active.

2.3.3.2 Simple ALOHA Retransmission Control

Packet reception may be confirmed in two different ways. The term ’end-to-
end’ confirmation is used when the higher level processes or programs doing the
packet transmitting and receiving positively acknowledge the reception of a new
packet. The other confirmation of successful transmission comes from the
transmitter’s own receiver and its collision detection circuits. Collision
detection circuitry does not guarantee safe reception at the final or ultimate
receiver, but it does permit the transmitter to immediately reschedule a packet
if it is known to be in error, thus avoiding positive acknowledgement timing
delays.

The exact procedure for “waiting a random amount of time” will now be
described. This procedure is used for the simple ALOHA protocol because it is
consistent with the closed-loop method which follows below.

A station which has determined that it needs to retransmit first waits for
the channel to go inactive. It then picks a random number in the range 0 to l,
and if this number is less than or equal to Pr(i) it retransmits immediately.
If the number is greater than Pr(i), it delays tau seconds, picks a new random
number and repeats the test. This cycle is continued until the retransmission
occurs.

By using some mathematical tricks we can simplify the above series of
tests and still achieve the same result. Again, we wait for the channel to go
inactive and then pick a number in the range 0 to l. The time we should wait,
twait, is then given by the following formula:

twait = randomenumber * tau * (1-Pr(i))/Pr(i)

The value of twait may be rounded to the nearest tau seconds. If the channel is
busy when the time delay expires, the station should wait for the channel to go

inactive and then transmit immediately.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 9
Level 2 Interface: Packet Transmission Specifications

2.3.3.3 Simple ALOHA Control Parameter Values

There are only two parameters subject to adjustment in the Simple-ALOHA
control algorithm. Consult AMSAT for currently recommended values of control
parameters. Typical values for these parameters are listed below:

econd

tau Ss
Pr = 4

= 1
Pr(i) =

2-3-4 Control Using the S-ALOHA-CLC Algorithm

If the channel duty cycle becomes greater than 20%, then there is enough
activity on the channel to justify control procedures which will guarantee
better throughput under heavy loading and under varying load conditions. The
Slotted ALOHA Closed Loop Control algorithm is a method whereby the transmit
and retransmit probabilities Pn(i) and Pr(i) are adjusted to accomodate the
current channel load, the adjustment causing stations to wait longer when many
transmitters are competing for the channel, and then shortening the delay times
as traffic is cleared and channel conditions improve.

The key elements of the CLC method are these:

All transmitters are synchronized and start and end their transmissions
within fixed time slots. Each transmitter monitors the total number of
successfully received packets within a recent time period (the “history
window’ , measured in time slots), and also keeps a count of its own’ successes
and failures within the window. Each packet transmitted by station i contains a
control byte which reflects the current value of Pn(i) for that packet. The
Pn(i) values in each packet are recorded by all active stations and _ their
values are used in load calculations specified below. With the data thus
recorded, a formula is used to update, at predetermined intervals, the Pn(i)
and Pr(i) for the station. Increasing values of Pn(i) or Pr(i) imply that every
station in the net is having more success and that less delay is required
before transmit and retransmit attempts. As the values of Pn(i) and Pr(i)
decrease more delay is introduced causing all stations to slow down, thus
reducing channel congestion. The following sections give the exact details of
the method.

2.3.4.1 Closed Loop Control Assumptions

This method assumes that channel time is divided into fixed periods or
slots, where each slot is ts seconds long and can contain the maximum length
packet plus transmitter startup and shutdown time. All slots will start and end
on the second’s tick from WWV.

Each active station keeps certain statistics over the last W slots and
updates its control parameters every UC slots. The update period, UC, will be
less than or equal to W.

The station must monitor the channel and count all successfully received
packets S. It must also count its own successes S(i).-

Finally, at each update interval the station must compute the weighted
average of current gate values. The current Pn(i) value for each station is
transmitted in the packet in the protocol load control byte which is the byte

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tions $ne amofteata svi‘ton fie vd bobsosex sus deiie'st. foes ut ‘eonlev (t)ot
duds s#6b of3 AEM «woled baftiosce enottsivaealss bank at baeu 518 aeulav
(Kyat oft .etevrotnt benivusteahsrq te .sisbqy o3 boau et Siuirot ¢ ft ~babvoset
(rave tsdo ylqmt (F)xT xo (Pat to eovlcy geteseroal -noitesa edt rot (t)9¢ dae.
bettupey 2f yanked aeet Jatt “bane a9 2am 37COMt aoived ef ten aut mk. noris3s
~etqas3ie iimecstist hos - Lites 2 sToted

auilt ,awob wole o7 apottsie [fs eiteyso bstuboxsat at ates. stom abnotosb
to alistoh topxe offs ovis itionas guiwoife? sal as okse0gme> ‘one guipubex
ii 33m oft

enos3 mea Loy eae sat kul batt Pie

TO eboltsq ‘exit? otnt Pebivib ef sali fomnmads ted4 ediag Cpinekn ate
igeel wintsem offs oatetqos mp0 bes reol absoxee at at idle done 2 on ,2tole
$s. 7 aulq toclosq

hue bis stete Lite etole (1A amis awohtude bus quaisde’ to a0,
ue a a . . <ViW nics a ofa to.
Pe ; ) , et "

aa 9 att eotshqu
Tau aFe. eds sao!
mrt

Com iis amy02 Nas pads’ age. |
i a ee oy 2 aorsedoua mo a

ihe sam otaase int tei
Vv (Let saesu. of?
tnos bao! Lox

: i. f ‘1! 2
ees Bhi : ? 4)

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 10
Level 2 Interface: Packet Transmission Specifications

immediately following the HDLC control field. The right-hand 7 bits of this
byte divided by 128 represent Pn(i) for that packet. Use of the high order bit
is reserved and it should be set to zero. Stations which are not using closed
loop control will set this byte to hex ‘00’. The weighted average gate value,
P, is the sum of all received Pn(i) divided by S.

2.3.4.2 Closed Loop Control Algorithm

The following formulas must be used by each station to update Pn(i) and
Pr(i) every UC slots.

(a) Estimate Collisions:
If C(i) = S (i) = 0 then:

If S = 0, let G = 0 and go to (c)
Otherwise, let G = 1 and go to (c)

Tf CCi) > 70" and S01) Sei0 ‘then:
Let G = Gmax, P = min(P,Pn(i)) and go to (c)
TE Sti) 4>00) then®
Let Cs = CU) o*9o7/ S(1))-and 'so.'to (b)
(b) Estimate total channel load G:
G= (S +C’)/W with 0 <6G < Gmax
(c) Derive new probability gates:

Po =) (Ga=31) -* "DP 0 Pn(i)

JA
-—

Pn(i)

JA

Pre)

JA
—

Pr(i) min(Pn(i), Prmax) 0

JA

2-3e4-3 Slotted ALOHA CLC Parameter Values

Consult AMSAT for currently recommended values of control parameters. The
following are typical values:

ts = l Slot size in seconds

W = 64 History window (slots)

UC = 16 Update period (slots)

Pn = .5 Initial new packet transmit gate
Prvimie Initial retransmit packet gate
Prmax = .5 Ceiling value for Pr(i)

DP = .25 Probability increment

Gmax = 2 Ceiling value for G estimate

[Some simulation studies are required to properly analyze the effect of changes
in the control parameters and to determine which features of the protocol are

really useful and which can be discarded. Here is a list of some questions
which need investigation:

ee Ue PN OSE

14 ee Nae oe. RE eb. os e
Ae, ey Reece Ain re ak f
Shee e Ee om Foods oe cao < ae Pau

‘ht
ma) os oy has ((t)ag iach J a0 aD cod

ee ae ie an nae easife 0 < (hye tf

fd) oF og ‘bre ee \ 2 EID 25D gal

6

i

iy . . oe ee bro! femme da duans’ etamisged (sd)

Bi Rett) > D> 0 dtiw WCO + 2) eu
py, 0 #29958 CibLE dail wo svirtesd (3)
At ' _ sil al, iv
ite + eee Be | sd ({ - 9) + (e08

i> E(B 2 200 (reins eee “am = Li}st

19

Pa ae iene "oul aptocmast DAHON bo 90f2 ¢.9.2~<

ta

aah «21979 eq ferseng, to O50 Leys Sebaearase ha ceo tol TAMA tigenod
A I dd old seabtey: totes one grivwol lok

a. py Pn \ am '
by Me ry

| F «2 gt
i aa ah
ih, «Ot iY
t. = of
re at

| eT
sit doktdw

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE
Level 2 Interface: Packet Transmission Specifications

1. Performance curves for Simple ALOHA
ae Effect of changing packet length.
b. Effect of carrier sensing.
ce Variations caused by changing Pr(i).

2. Performance curves for S-ALOHA-CLC
ae Effect of changing packet length.
b. Effect of carrier sensing.
ce Benefits of slotting.
d. Parameter settings and optimal values.

3. Determining the optimal load level to switch from
the Simple-ALOHA to S-ALOHA-CLC.

The simulation could be written in PASCAL using discrete time steps.]

"

Saree,
Ae

ao

ALG

: -

a ~” soaive a bev gat ashes ire |
Hh are hee cand oF Ast

- rh Lane. eT an a i OE ea s
YW hee i Phy
or: 2900 ‘ont adeno tb: b gnaw 40208 wk. soidtay od 6b! isp te odT :
; " De 7 Ai ' bs
Wear |e f ; ‘oe . Ae a. : ul
Ve ie ety
N , » ye Ain a , i
4 ] A) De f * , aos 7
} y' } >. ba : he ; bal
: , i “ .
i } : ir cn { =
; cy, any
4 / 2 ’ @ w
4 4 am
(a » : ~~ mh
' <
’ oe j
’ ay. : 4
7 . fF ¢

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 12

Chapter 3

LEVEL 3 INTERFACE: NETWORK SPECIFICATIONS

3.1 Datagram Network Characteristics

The architecture of data communications networks in use today is diverse
and many different types of connecting arrangements are possible. There are
point-to-point connections, multi-point networks, switched circuits, virtual
circuits, switched virtual circuits, etc. The AMICON network is one example of
a fully-connected packet switching network. The term fully-connected is used
because there is the possibilty of a connection from every station in the net
to every other station (through use of the multiple-access broadcast channel).
The network is a packet switching network because all user information is
broken into small packets of data, allowing many different users to have
multiplexed access the channel.

The technology of building packet switching networks is under active
development currently, and there are many different types of packet switching
services available today. The type of service that best characterizes the
AMICON network is referred to as a datagram service:

A datagram is a self-contained packet which carries sufficient information
such that it can be routed from source station to destination station without
reliance on any previous exchanges between source and destination and _ the
communications network. The data field within a datagram will be kept intact
and not split-up or altered in any way by the network.

The delivery of a datagram is not guaranteed. There is a high probability
of delivery, but it may occasionaly be lost. The data within a properly
received datagram, however, will have an extremely low probability of error.

The sequence in which datagrams are supplied by sender is not necessarily
the sequence in which they will be received by the receiver. All datagrams in
transit in the network are treated as independent entities.

Under some circumstances it is possible for a duplicate transmission to
occur, causing the same datagram to appear more than once at the receiver.

In summary, a datagram service is an extremely simple but fairly fast
transport service which serves as the foundation on which higher level
communications protocols are built. These higher level protocols (Level 4 and
above) are responsible for end-to-end acknowledgments, sequence checking,
retransmissions of lost packets, flow control and other controls which will
guarantee a complete and orderly passage of data from sender to receiver.

3.2 Packet Format

The packets or datagrams flowing through the AMICON network will have the
format described below:

95 gyda? -oldiagog

pt oltserolak 1380,

servi ne mabe pap ak) Fie oe) obteoknstat aed to 9 didots oat
| a1 an eng grbinetaos To soges. sae, nem, a
Tautthy .sdivowks berios wa <adrowion drkogeis fom vor tbeanes Imboq~od~3 coq
to elqwaxs gn0 et Iiee ssa THA. eet . ote ebtl poxio fewstty battog bwa fal
heey @b botoenagon ence t oat saowter gatiotive ialosg, betoonnos~¢lini |
jen 983 nt motte Bde | “itor? moktoeqnos i ze yo 1Fatedag, em) @) ‘oxscts. samen
* (lemnets 2 faspbaoid | f ti te seu dawordt) aokgsse todto cisve ot
finer: gpebiina be isatoeq pn ak srowion oat
ave! os arsay stg 9923 bb cess 4 fe 463e6 to atotond iisme otmt sasiord
ra Mint * Lavendiiti ad eesons hexoiqis ium
avisos' tober et ‘eaixoucti silicones sang got bitud te ‘Cao font: ‘a3 nT
grifotiwe tefosq to Boggs Faeteti lb yasm ese stels brs eUiaqeTIwo tnemqoloveb
ats gositresosyads | gaod isttt ontyree es sqyt aff .vebor olde! teve eestvree

ieakvies Witgatsbh a 2s 0 berEBast at Jrowdem MOOIMA

cok pamro tnt ne a pn fistiw jotosq heristnoo-Iles s at pergsgs
tuottiw cnotis:a soLteat3zeeb 63 nolkisiea sores mo1l bejves,s0 mao 3k Jed? dgus
et}. bas moktcnizash bas somos nogw-tod eanineshitell au olwetq yas ao sonntlos
toptak tqod od Jiiw mtgeieb @ stdtiw bier? ctsh edt - dtow ton enoki sok mymines

poner eft vd vaw yrs ci beretis wo qu~diige ton brs

Uti bide dorg deta & €i oxodT sbegtneyeug Jom at omigsteb 5 xo yaevbish oHT

wineqotq s nidvio sieb aft’ -teof od Yissotesooo yam ae aud .Vaeviteb to

+ OTT Yo. yi i¥dsdorg wol yienetixse re sve Iftiw . Tevewardl cau Tyeag® bevisost

ylixseaesson jon at Gesdebiains vd bet beni Ais Bm tg2 teh dobster at soastpse ont

at smevgeteb [1A .revksst oft yd bevisoax ad: Sitw ysds oid nt @@menpse sis

sasivizne gnrobasqsbal 2: botsous S58 Wrouten sd3 mi Dheras3

a
i

ot solegimessis stnotieut s tot Lge at si asonasamaxts emon yo ball
\ a »tevisoet si3 26 990 neds exo" taeqgqe oF Bie ie a" ison tte

seat vitka? wd siqmte ylomeisxs os at SORAER a8
Ievel ‘rorngtd adoidy io moltsonscl of ae
bas A feved) efosodoxy Level toigtd 92s Sat 4 bbe a8
e&stidoado sonsupoe | <paromgbe Ivoml! ss bine 9~0F—BAS |
ffiw dotdw alorsmon radgo bos fossnos volt aden

eravieoot 3 1 el ost ‘Bieb to SRRRREI,

ae
0, Ae ob sn imo
aa S16 (svecin
Rime ne TI 97%
r > 8 So105 18S

Y a

Pi er rf. ] e me ; ‘ii : i fs ‘ ‘a oe ; nd

7 iit) e ne
. eh

U

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 13
Level 3 Interface: Network Specifications

Bytes Field Description
1 ton Framing Initial framing or synchronization bytes
1 Address HDLC address byte
1 Control HDLC control byte
1 Protocol Protocol load-control byte
1 to n Receiver Receiver Call Group Field
1 “=” Separates Receiver Call Group from Sender Call
1 to n_ Sender Sender Call Field
if fs 4 Terminator for datagram address fields
0 ton Data Datagram data field (unrestricted in content)
2 CRC Packet checksum bytes
1 ton Framing Terminating framing or pad characters

The initial framing or synchronization bytes are not detailed here. The
beginning-of-packet control sequence is described in the Level 2 description of
a packet.

The HDLC address field consists of a single byte. Use of extended address
fields, as provided for in the standard, is not recommended. The contents of
this address field are not used by the Level 3 protocol. Packets which are used
for testing should set the address byte to hex °00%. Packets which are not
using the address byte for higher level protocol functions should set this byte
to the all-parties-addressed code, hex ’FF’.

The HDLC control field consists of one byte. Use of an extended control
field, as provided for in the standard, is not recommended. The contents of the
control field are not used by the Level 3 protocol. Stations not using this
byte for control purposes should set it to hex ‘°’03°, which is an HDLC
Unnumbered Information frame.

The protocol load-control byte is used by the S-ALOHA-CLC protocol control
software. The contents of this byte are detailed in the Level 2 description of
the closed-loop-control algorithm. Stations not using closed loop control
should set this byte to hex ‘00’.

The receiver call group field is a field which contains the call or calls
of the receiver of the datagram. See Section 3.3 below.

A 7

The single ASCII character “=” separates the receiver call or calls from
the sender’s call. See Section 3.3 below.

The» sender’s.call .field.,is..a,.\field» which scontains the call”-of “thé
datagram’s sender.e See Section 3.3 below.

aie es ; jer
: aie Ph, Yaa - beta 9 b]
foc iy A eee ' ' , .
Hp. hat oa ae vd
‘ Pale sabyoe ft 02 L .
ala ok basot-vteonmy) biog? eo misgoaer Seat a 03 9 )
LT ueiiitA Nae hat ol obaed: sistas, jadoe4 a. S Dae
’ | eh S293 SB IBD beg 0 satan grctenters’ | guimssi on Ose

oft) ‘sored be ttetab Sonar asted | mobi es. tnosdonve 31> geimaii Jetsral ) eit
to mola its ee g dyer ody BB “ho dttsaed st eamsupse foxjaoo isdopq-io~gainatged

ay. ae ‘ i rs aa 5.

La Lon S ; 4 : ’
gagahbe babnd: ho ‘ea oe aigire B 30 etelanos Biéhi eastbbs OMG oft

bo e3netg9o9,.9 Pee: upamaes Jom ai .brabrsde oii nt set bebkvomqe ee -ebistt

baen ore Ain tds sonia ‘~hosojoxg F. Javal eft xd seit jon 938 biel? eaorbbs eid

jon 9p Aotsw aiset 00", xed of sayd arortbha odd 398 bloode sakiesa 102

oad: ait tessa artobs mir? Tos oerg favol sodgid sot otyd eseabbs 9o1l3 ‘poatey

i ‘a oe . is i za .2bo besesabba—aot oS si3. ot:

U
|

Soca seed a0 to esses: bistt £ Aecelai IIH, oT

+t ve a b ba: aon + don ei ,byehnnte off nk x01 bobivoug es .bisti
iy eno. i832” C trodauny € Ievel d+ yd bseu tow avs S¥sti Toriaoay
dite ee * edt (a3 3% 4ez Ridosda asboqiug jTortnoo* x02 sivd :

a

ome 1? noljsatot al borsdmuany ..

gH? @d beau 4? sivd fotanod-hsok foroserq sit
vat Delisted 9%a sa¢d aids I¢ canstmos Sat .stawitoe |
: oni BAO ISI smdotsog fe fo xtnoo-qool=beeolo oAy

) : OB] xen ha oro sidjpsee blyode

al tise ‘gat ito ta ‘quox kaa sykeoet oct
Pte paomciel wee “hi taal ant to revere” ort 26

f ‘ i
eae in 5 Ye t3), Rit qagk | red5, rines m abanig, ear |
pm oh / am * Nae iia gare ane agi tose" 982. anarigs sabres ea
a A ara Ug GO Vieni 0 8h a OR ee }
ra ee et _ bod? fore "abies at ‘

oi tD92% o92, sxebape a” msn 38B a.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 14
Level 3 Interface: Network Specifications

The single ASCII character ’;” terminates the datagram addressing fields.
See Section 3.3 below.

The packet data field is described in Section 3.4 below.

The two cyclic-redundancy-check (CRC) bytes provide error checking for the
contents of the packet. The contents of these bytes are detailed in the Level 2
description of the packet.

The terminating framing or pad bytes are described in the Level 2
description of the packet.

3-3 Packet Node Addressing

The datagram addressing field starts with the byte immediately following
the protocol load-control byte, and ends with a semicolon (;)- The function of
this field is to specify the call of the sender of the datagram and to specify
the call or calls of all intended receiving stations.

A point-to-point datagram is a datagram which is intended to be _ received
by one station only and which should be discarded by all other stations.

A broadcast datagram is a datagram which is to be received by all stations
currently listening to the channel. A datagram containing a CQ or a bulletin of
general interest would be typical examples of broadcast datagrams.

A multi-cast datagram is a datagram which contains information intended
for a selected group of stations having a special interest in a particular
topic or participating in a net. The multi-cast group is specified by one or
more “general call’ group addresses and optional qualifiers as outlined in
Sections 3.3.3 and 3.3.4 below.

3.3.1 Packet Node Addressing Syntax

The datagram address field has the following general form:
Receiver=Sender ;

The Sender is the call of the originator of the datagram. It is a specific call
having the syntax outlined in Section 3.3.2.

The Receiver field specifies the station or stations to which the datagram
is being transmitted. The Receiver address field contains either a single Call
Group or several Call Groups separated by commas. Each Call Group may have an
optional qualifier. A Call Group is either a Specific Call Group (Section
3.3.2) or a General Call Group (Section 3.3.3). Examples:

Receiver1=Sender ;
Receiver 1,Receiver2=Sender ;
Receiverl.Qualifier,Receiver2=Sender ;
Receiver 1.Qualifer, Receiver2, Receiver3.Qualifier=Sender ;

The ASCII ’=’% character separates the Receiver and Sender fields. The ASCII
semicolon terminates the datagram addressing field.

fe, ot teaqe B em, ar sasagnssh ait to sesamin any Re.

dood o~cone ban be
pauline sit “4

| : beg ‘a gone nisoolarss oft
s toto “te reaahe ob

a ey

goiwotte? vlosatbomay nary oa” adie State bisit sntheneiion icatiaia ss wee a F
Ro noisome? off .(;) Polooima o di3bw ebro bas .etyd Loxidop-bsol fosotorq offs

| vtiosge of bas maannanes oni’ 20:39 st

2 > gels fo [feo act vPeeqe oF et blot? aids
venokaage: ati aoss ba baositt ils to alino 10 Liss oda

bavtose ‘sa 03 ee et ‘Poker argent S al os mesa’ apkognos ~tnkog A

~erobwase wefto [fs yd Sebuwiie th sd Sivoda dokdw aid 1 coil HOT SESE, ano Yd

enot feta fia: ed bavtsoon sc od ek re metgeteb s et a5 tap feb nan niid A

to sisetind s to O09 a getatasaoo meigsish A .lonasds sd3 o% gainetetl Yiinoxwws

- .Shntgedeb er ae éatymsxe Inotayt od: biuow resets intensg

bebodieck rotsamrotat ‘Mpeasdiee dokde gsiveish s et mB% sails sense sinc AS
tejyoliyag &® nmi Jesyeyat feisoqs 5 gotved enoktaie te quotg betostea s yoi

30, 980 Yd betlioaqe at quotg Jasorisiue off «ton & at. gniteghoit1sq nis) siqos

* boi tayo (Os ausibiterp Ismottgqo bas eotbhs quorg “liso fsornsg * Son
TAP swoled hidink. bos f £6 erottose

xBI oye wi tegs) 20 oe desks d ist. €

imrot Imsoneg getwollot edt ead blot? esos amtgsze! sat

2 wbmee=tevisoal aoe =
m Ais ae ew An

32 oft Bt hiss: oAT
: quo zeta al erivss

ee.
i

eR e£2E cottose al .

ih lpi iliac abs aren To mokinite ol eotitssqa i at ao nsdn he
ALRITE Rete | enksdoo bisit aecribbs zwvioass OW? «1 ; ti oe ge | vated 7

= Oven vba quo) Sisl: ios sesmon yd bejsisqon aquet) [fe fersavee 19 aquoxd
aks, 2) ide ffso ott tcog? & vad3teo «at quord lisd A SEL Enka ka ve
me eh, 4 Peptganst 2 {£48 ae aottaee) que: a . Lapaden 8 0 (St 4
Ps | te tL, my i ; tobret=Iteviessk by «}
ae | g7Sbaee=Sxevisced J sovtesad
i _pepechinninglee nim tet ie an

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 15
Level 3 Interface: Network Specifications

3.3.2 Specific Call Group Syntax

A Specific Call Group is the call of a specific, individual station. An
optional qualifier may be suffixed to the call (See Section 3.3.4). Lowercase
ASCII characters will be converted to uppercase by the program scanning the
Call Group. Any ASCII space characters found in the Specific Call field will be
discarded. An ASCII slash character, ’/’ , may be appended to the call to show
portable operation. If the specific call is used in the Receiver field, it may
be preceded by a negation operator (See Section 3.3.3).

3-3-3 General Call Group Syntax

A General Call Group is a specifier which allows a sender to transmit a
datagram to a group of stations. It is the mechanism which implements the
broadcast and multi-cast modes of packet addressing. Whereas the Specific Call
addresses a specific, individual station, the General Call allows construction
of address templates which are not specific, and which may be used to match any
number of individual calls.

The key to constructing a General Call address template is the use of
certain characters which are ’wild-card’ characters, that is, characters which
will match one or more letters or numbers in a text string. Two wild-card
characters are now defined:

The character *?” may be used to match any other single letter or number.
For example,

KL7???2 matches all Alaskan 2 x 3 calls
W1?BC matches WIABC, WIBBC, WICBC, etc.
VE???2 matches all six character VE calls

The character “*’ matches any string of numbers or letters including the
null string. For example,

* matches every call in the world
W*]* matches all W calls in the first call district

The characters °?” and °*” may be intermixed in any manner in creating a
template. All lowercase letters will be converted to uppercase-e Any ASCII
blanks embedded in the text strings will be discarded. A receiver scanning an
incoming General Call Group should accept the datagram if the receiver’s call
matches any template given in any of the address fields in the Receiver field.

If the General Call Group is preceded by a minus sign, then the datagram
should be discarded if the receiver’s call matches the negated address
template. For example,

* , -KH6*=KH6XYZ ;

is a datagram addressed to every station listening to the channel except any
other KH6 stations

te ; ¥ 4 ss ,
one =n ot weg TT : . :

mes stand 85

ee tesobs ord

If & feten I 9: yh Behl Sfifoeqs & sseaerbhs
BOT o ae iskte bere. co doa Ste Hoke ‘eetsiqnas 2207bbr to
ee es ei ek a a

-allgo Ian bivibat tO tednmin

“~
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| ib cdanengy ey i “pxaai-blse* om ites eipasetarta, nist199
S¥0m ITO 219 dsteam Lf te
" thentigh Won Sts 839496 15d >

mt

4 1 xe > r9g3e! stants reitt0 vom G59Ro1 64 bea oY vst “S$ 18josted. edt.

iopid .Siomexs +07 |
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ea wlG hem ale op "#938 POGIIW .47I 0 OGALW eadstem - JES IW
Wats ay i. : ieee nied bal tes5siels vis Pts 29rotom SPtay

Mare

ods gate loa ‘exs3teL to etd dete te gatvse yas corstsm “** xSiasisdo silt
timxe ‘oT .gnbase [ine

binow oft nb Ifs5 Yisv9 sedate %
“sabia thao JevkT ad? ot alis> WEin Babstee | Aimy

BO Wsre. ar boxtorisaat of van *** ban *P" extetasteds oft
MISqqu oF beste vir0s od fliw exssitet o#eitewol Ifa .stelawcs
head Iftw egobrse Jxet shy at _hebbedms mia ld

2d mergs3eh of3 tg9998 blnede quot ited fsvonso strane: vat
at obtent seerbbs oat? te vs ok mevig stelqmes yas 2o:!575m

aka id ee bobesatg at quo Tle) isxenod 6d. 37
| Als e*yevissay ais ir’ bebteoet EB of binods
eae . <Sigapxs 0% -stelqmes

‘ale ran gp sat

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 16
Level 3 Interface: Network Specifications

3-3-4 Call Group Qualifiers
Each Specific Call Group or General Call Group may optionally be followed
by a qualifier text string. The function of the qualifier text string is to

restrict very general call addressing to specific stations by functional

interest, mode of operation, or any other criteria which may be agreed on by
two or more stations.

A qualifier text string begins with an ASCII period and immediately
follows the Call Group. The text string is terminated by a comma or the equal
sign separator. The following are some examples of qualifiers:

-CQ The datagram is addressed to any station matching the Call Group
which wishes to establish a connection with a new station.

-SSTV The datagram is addressed to the specified Call Group and
particularly those stations interested in slow scan TV.

»AMSAT To stations interested in receiving AMSAT related bulletins.

eNTS To stations handling formal message traffic.
exNET To stations belonging to net x.

A list of commonly used qualifiers will be published by AMSAT once their use
has been established.

3-3-5 Call Group Addressing Examples

The following set of examples demonstrates some of the possible legal
combinations of the above Call Groups and Qualifiers:

KIHTV=KA& ;
A point to point datagram from KA6M to KIHTV.
* .QST=W1AW;

The datagram is a bulletin from the ARRL addressed to any station interested in
the latest ARRL news.

* .CQ=WA2LQQ;3
Station WA2LQQ is calling CQ and looking for a new contact.
AX ,K* ,N* ,W*=KA6M 35

A datagram intended for U.S. stations only. Will also end up in some rare DX
locations.

* .DDX=W3IWI;
To any station participating in the digital DX data contest.
K1HTV, W6S P, W6X0 , WA2LQQ, * -AMSAT=KA& 3

A datagram to the specific stations listed and any others interested in AMSAT
related bulletins.

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 17
Level 3 Interface: Network Specifications

3.4 Packet Data Field

The datagram packet data field contains data or control information which
the sender desires to transmit to the receiver- The contents of this field are
not interpreted by Level 3 software. The only constraint is that the length of
the data field plus the control and addressing fields must not exceed the
maximum packet length.

[The addressing mechanisms described here are general enough to construct
practically any desired subgroup. Addressing specific countries or geographical
areas, though, leads to some “Skward constructions and it would be worthwhile to
invent some mechanism to make a geographical target area easier to do.]

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 18

Chapter 4

LEVEL 4 INTERFACE: APPLICATIONS

[There is some question whether applications standards should even be proposed
at this time. It may be much too premature and perhaps it would be better for
users to have some time to experiment first.]

4.1 File Transfer Protocol

The transmission of complete files through the network will not be covered
by this revision of the specification and is a subject for further study.

[ARPANET uses a file transfer protocol known as TCP. It would be a good
starting point and perhaps we can adopt a compatible subset for our usee- The
original reference material for TCP may be found in ’A Protocol for Packet
Network Intercommunication”’ by Vinton G. Cerf and Robert E. Kahn, IEEE
Transactions on Communications, Vol. COM-22, pp- 637-648, May, 1974.]

4.2 Graphic Standards

The transmission of graphics over the network will not be covered by this
revision of the specification and is a subject for further study.

[Should AMSAT even attempt to define a standard?]
4.3 Image and Video Transmission

The transmission of video images over the network will not be covered by
this revision of the specification and is a subject for further study.

[Should AMSAT even attempt to define a standard?]
4.4 Digitized Voice Transmission

The transmission of digitized voice packets over the network will not be
covered by this revision of the specification and is a subject for further

study.

[Should AMSAT even attempt to define a standard?]

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE

Appendix A - Selected Bibliography
REFERENCES ON PERSONAL COMPUTER NETWORKS

A Multiuser Data Network - Communicating over VHF Radio
Bruninga, Robert E., 907 Ninovan Road, Vienna, VA 22180
BYTE, Vol. 3 No- 11, p- 120, November, 1978

Design Considerations For A Hobbyist Computer Network
Caulkins, D., 437 Mundel, Los Altos, CA 94022
Proceedings of the First West Coast Computer Faire, ADELE L977

PCNET 1979
Caulkins, D., 437 Mundel, Los Altos, CA 94022
People’s Computers, Vol. 6 No. 2, Sep-Oct 1977

Hobbyist Computerized Bulletin Board

Christensen, Ward, 688 E. 154th St. #3D, Dolton, IL 60419
Suess, Randy, 1930 Bradley, Chicago, IL 60613

BYTE, Vol. 3 Noe 11, p- 150, November, 1978

Community Memory - A “Soft” Computer System
Felsenstein, L.
Proceedings of the First West Coast Computer Faire, April, 1977

Homebrewery vs. The Software Priesthood
Fylstra, d.

Wilber, M.

Byte, October, 1976

Distributed Network
Horton, Glen, Hickock Teaching Systems, 2 Wheeling Ave., Woburn, MA 01801
BYTE, Vol. 3 No. 11, p- 62, November, 1978

The Sky’s the Limit: Ham Radio for Intercomputer Communication
Kassar, Joe, 11532 Stewart Lane, Silver Spring, MD 20904
BYTE, Vol. 3 No. 11, p- 48, November, 1978

The Club Computer Network
Kassar, Joe, 11532 Stewart Lane, Silver Spring, MD 20904
BYTE, Vol. 5 No. 5, pe 202, May, 1980

DIALNET And Home Computers

McCarthy, J.

Earnest, L.

Proceedings of the First West Coast Computer Faire, April, 1977

Why not Just Use the Phone?
Newcomb, Donald R., 819 Bayou Blvd., Pensacola, FL 32503
BYE oevOuse 3 NO /,upeni2)l, July,) 1978

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1-01 PAGE 20
Appendix A - Selected Bibliography (continued)

CB Computer Mail
Pank, R.
Proceedings of the First West Coast Computer Faire, April, 1977

Satellite-Linked Computer Network, A Phase-III Hook-up for Your Keyboard
Riportella, Vern, WA2LQQ, AMICON Coordinator, Box 56, Warwick, NY 10990
HAM Radio Horizons, March, 1980, pp. 48-51.

Personal Computers in a Distributed Communications Network
Steinwedel, Jeff, W3FY, 715 Reseda Drive, Apt.2, Sunnyvale, CA 94087
BYTE, Vol. 3 Noe 2, pe 80, February, 1978

Calling All Computers
Stoner, Donald L., W6TNS/7, John Hancock Bldg., Mercer Island, WA 98040
BYTE, Vole 3 Noe 12, p- 159, December, 1978

Computer Networks
Tesler, L.
People’s Computers, Vol. 6- No. 2, Sep-Oct 1977

A Network of Community Information Exchanges: Issues And Problems
Wilber, M
Proceedings of the First West Coast Computer Faire, April, 1977

CIE Net: A Design for a Network of Community Information Exchanges -- Part 1
Wilber, Mike, 920 Dennis Drive, Palo Alto, CA 94303
BYTE, Vol. 3°No. 2, ps 14, February, 1978

CIE Net: Protocols --— Part 2
Wilber, Mike, 920 Dennis Drive, Palo Alto, CA 94303
BYLEs VOM s 3 NO~ 135. p+ loZ,eMarcie e975

CIE Net: Other Considerations -- Part 3
Wilber, Mike, 920 Dennis Drive, Palo Alto, CA 94303
BYTE, Yok. 3 No« 4, p- 168, “April, 1978

ASCII at Last?
Williams, Perry F., WIUED
OST, Vol. LXITt No. 10, p. 5458 0ctober, 1978

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 21
Appendix A - Selected Bibliography (continued)

REFERENCES ON SATELLITE PACKET COMMUNICATIONS

The Throughput of Packet Broadcasting Channels

Abramson, Norman

IEEE Trans. on Communications, Vol. COM-25, No. 1, January, 1977, pp- 117-128.
Reprinted in "Satellite Communications", Harry L. Van Trees, Ed., IEEE Press

Closed Loop Stability Controls for S-ALOHA Satellite Communication
Gerla, M. and Kleinrock, L.

Proc. Fifth Data Communications Symposium, Snowbird, Utah, September, 1977.

Satellite Packet Communication - Multiple Access Protocols and Performance
Lam, Simon S.
IEEE Trans. on Communications, Vol. COM-27, No. 10, October, 1979, pp. 1456-1466

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 22

Appendix B —- ISO Specification 3309

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 23

Appendix C - Datagram Addressing Syntax Diagram

ie?
GC)

SPECIFIC CALL }

QUALIFIER

ies:

SPECIMIC CALL |

af GEVERA caALL +

AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE

Appendix D - Distribution List

Col. John Browning, W6SP, AMSAT Board Chairman
6202 Lochvale Dr., Rancho Palos Verdes, CA 90274
Home: Office:

Dr. Tom Clark, W3IWI, AMSAT Director & Executive Vice President
6388 Guilford Rd., Clarksville, MD 21029
Home: 301-286-3113 Office: 301-344-5957

Mark Corbitt
6568 Beachview Drive, Noe 311, Rancho Palos Verdes, CA
Home: Office:

Dr. John DuBois, WIHDX, AMSAT Special Systems Consultant
241 Crescent Ave., Waltham, MA 02154
Home: 617-263-7004 Office: 617-891-9029

Gary Fariss, W6KYF
18983 Saratoga Glen Place, Saratoga, CA 95070
Home: 408-257-0948 Office: 408-734-6857

Gary Hendra, WA6SUW
3249 Lantern Court, San Jose, CA 95111
Home: 408-629-5863 Office: 415-494-7400 x6280

Mark Kaufmann, WB6ECE
14100 Donelson Place, Los Altos Hills, CA 94022
Home: Office: 415-948-3777

Larry Kayser, VE2QB
Ottawa, Canada
Home: Office:

Doug Lee, K6TDR
225 Nes Clark, Ave-; Los Altos, CA 94022
Home: 415-948-3601 Office: 415-326-6200 x2418

Wally Linstruth, WA6PJR
2413 Burritt Ave-, Redondo Beach CA 90378
Home: 213-542-3290 Office:

Dr. H. S. Magnuski, KA6M, AMICON Network Consultant
311 Stanford Ave., Menlo Park, CA 94025
Home: 415-854-1927 Office: 415-856-7421

Howard L. Nurse, W6LLO
665 Maybell AVe-, Palo Alto, CA 94306
Home: 415-493-0371 Office: 415-732-2710 x2559

24

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AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE
Appendix D - Distribution List (continued)

Gary He Price, W6IRA
Home: 415-732-1008 Office: 415-326-6200 x4820

Dr- John Pronko, W6X0, President, Project OSCAR
230 Hawthorne Ave-, Los Altos, CA 94022
Home: 415-941-6988 Office: 415-493-4411 x45179

Vern Riportella, WA2LQQ, AMICON Coordinator
Box 56, Warwick, NY 10990
Home: 914-986-6904 Office: 201-768-2500

Bob Rouleau, VE2PY
1050 Churchill, Mt. Royal, Quebec H3R 3B6
Home: 514-341-7806 Office:

Re Satterlee, WB6VAL
1212 We. McKinley, Apt. 5, Sunnyvale, CA 94086
Home: 415-969-4451 Office: 415-964-5700 x227

Paul Zander, AA6PZ
86 Pine Lane, Los Altos, CA 94022
Home: 415-941-7821 Office: 415-857-3776

Rich Zwirko, KI1HTV, AMSAT Director and Vice President
34 Montclair Dr-, Manchester, CT 06040
Home: 203-646-5726 Office: 203-522-1080

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"AMICON SYSTEM SPECIFICATION -- Draft Revision 1.01 PAGE 26

—<—— NOTES --~-